In recent years there has been an increase in the use of optical fiber communication networks. In an optical fiber communication network, an optical transmitter takes an electrical input and converts it to an optical output using a light source (e.g., laser diode, Light Emitting Diode (LED), etc.). The light from the transmitter is coupled into an optical fiber and is transmitted through the optical fiber to an optical receiver. The optical receiver converts the light back into an electrical signal.
Early optical fiber communication networks used transmission of one bit of information per data symbol. However, due to the need for high-capacity communications, there is an increasing demand for higher bit rates. This has led to the use of higher order modulation schemes for optical transmissions. Modulation schemes that have been implemented include, for example, Quaternary Phase Shift Keying (QPSK) and M-Quadrature Amplitude Modulation (M-QAM), wherein M is an integer with the power of 2 (i.e., 2, 4, 8, 16, 32, 64, etc.). In such modulation schemes, the optical transmitter includes an optical modulator that modulates the optical signal to carry the additional data.